This invention relates to blue-green lasers and more particularly to an efficient four-level blue-green, excimer-pumped laser.
It is well known in the art that laser systems include three main components; the laser medium, which may be a gas or a solid; the laser cavity which includes reflective surfaces; and means for pumping the laser medium to an excited state. The laser medium may be optically pumped, or electronically or chemically excited and may be operated continuously or pulsed. Such laser systems may be operated at room temperature or at very low temperatures such as at liquid-nitrogen temperature. Further, laser systems may be operated in or outside the visible spectral region. They may be highpower or low power. Laser systems have been developed using a variety of elements, compounds, gases or fluids and all have one thing in common--they emit coherent radiation.
Laser emission in the blue-green spectral region has been reported in an article, "Stimulated Emission from PrCl.sub.3 ", by K. R. German et al. in Applied Physics Letters, 22, page 87, 1973. The subject matter involved a tunable pulsed dye laser pumped by a nitrogen UV laser, and a crystal of PrCl.sub.3 by which blue-green laser operation was achieved only when the crystal was cooled to below 14.degree. K. More recently, an article, "Blue Light Emission by a Pr:LiYF.sub.4 --Laser Operated at Room Temperature", by L. Esterowitz et al. in Journal of Applied Physics, Vol. 48, No. 2, pp. 650-652, February 1977, described room-temperature operation of a blue-green laser where the laser medium was a LiYF.sub.4 crystal doped with Pr.sup.3+ and the excitation means was a flashlamp-pumped dye laser. It has been determined that dye lasers have poor operational life for the excitation wavelengths required and incoherent sources have poor efficiency. Patent application Ser. No. 868,360, filed 10 Jan. 1978, describes a blue-green laser pumped by a XeF excimer laser. The XeF laser pumps a matching transition in divalent ytterbium which has an absorption band between 350 and 360 nm depending on the host material. The host crystal such as LiYF.sub.4 is codoped with Yb.sup.2+ and Pr.sup.3+ (the lasing ion). This laser system is a three-level laser which has better efficiency and operational life than prior-art dye pumped lasers.